Dyeing of polyacrylonitrile articles



United States Patent Or "ice DYEING OF POLYACRYLONITRILE ARTICLESHermann Egli, Basel, Switzerland, assignor, by mesne assignments, toSaul & Co., Newark, N. J., as nominee of Fidelity Union Trust Company,executive trustee under Sandoz Trust No Drawing. Application September20, 1954 Serial No. 457,310

Claims priority, application Switzerland December 4, 1953 16 Claims.(Cl. 8-55) According to experience, best results are obtained when thecuprous ions are formed in the dye-bath itself. For this reason, it hasbeen proposed:

(a) To react a cupric compound with a reducing agent in the dye-bath,preferably prior to the addition of the dyestulf. Such reducing agentsare for example zinc formaldehyde sulfoxylate, hydroxylammonium sulfate,glyoxal, sodium bisulfite, etc.

(b) A further method which, as hereinafter set forth in greater detail,is only of theoretical interest, consists in producing cuprous ions inan acid dye-bath by the addition of copper powder. a

As is evident from the technical literature, the method of operationdescribed under (a) is today the generally employed method. The dyeingis carried, out in the presence of a cupric compound which is reducedwith zinc formaldehyde sulfoxyl'ate, hydroxylammonium sulfate, etc.Where the dyeing is carried out by the high temperature method (dyeingat a temperature above 100 C., for example at 120 C., and at a staticpressure corresponding to this temperature), sodium bisulfite can alsobe used as reducing agent.

However, method (a) is bound up with various defects. Thus, for example,it must be borne in mind that zinc formaldehyde sulfoxylate can attackcertain dyestuffs. Another possible danger involved in the use'of thisproduct is the instability of thecuprous ion, which is readilydisproportionated to .cupric ion and metallic gcopper. This mode ofprocedure makes possible the production of copper spots on the textilematerial. This spotting of the textile material can be avoided byselecting another reducing agent. I-Iydroxylammonium sulfate presentsnodifil: culty in this connection since it is capable of building withthe cuprous ion a complex compound whichdoes not decompose. However theuse of hydroxylammonium sulfate results in a considerable increase inthe cost of the dyeing process. A further difficulty of method (a)resides in the poor controllability of the state of reduction of thecopper salt in the dye-bath. Too great an addition of reducing agent tothe dye-bath immediately produces too many cuprous ions, and this mayresult in unlevel dyeing. It has therefore been proposed in thetechnical liter ature to check the state of reduction of. the coppersalt in the dye-bath by constantlymeasuringthe redoxlpotential. As soonas a critical value is exceeded, further reducing agent has to be added.

v The second possibility, (b), of dyeing textile material 2,874,021Patented Feb. 17, 1959 of resinous polyacrylonitriles or resinous mixedpolymers of acrylonitrile and other unsaturated compounds by adding finecopper powder to the dye-bath, acidified with formic acid, is notmentioned in any of the large number of dyeing directions described inthe technical literature. This is understandable, since in practice themechanical soiling of the textilematerial by copper dust cannot betolerated, and the presence of copper dust in circulating baths is outof the question from the standpoint of the circulating pump.

The conversion of copper into cuprous ions is an oxidation procedure.Consequently an oxidizing agent has to be present if a dyeing whichrequires cuprous ions is to be produced with metallic copper. Tests haveshown that pure copper, in a closed bath acidified with formic acid,produces no dyeing. This can be explained by the fact that dilute acidscannot dissolve metallic copper in the absence of oxidizing agents,because of the fact that the potential of metallic copper is 0.3 voltgreater than that of hydrogen. Reports in the literature that dyeing has*been obtained with additions of copper powder are undoubtedlyascribable to the fact that copper oxides were present. However thequantity of such oxides is very small and very difficult to determineanalytically, and for this reason a technically satisfactory carryingout of the dyeing process according to method (b) must encounter greatdifficulties.

A primary object of the present invention is to obviate these prior artdefects. This object is realized, according to the invention, byproducing the cuprous ions necessary for the dyeing, by introducing thesystem Cu/Cu++ into the dye-bath. The surprising eifect of the systemCu/Cu++ is ascribable to the resulting equilibrium:

The resultant cuprous ions thereupon participate in appropriate mannerin the dyeing process and make possible the successful dyeing ofpolyacrylonitrile with water-soluble dyestuffs.

In one aspect thereof, the present invention is'therefore concerned witha process for dyeing articles of polyacrylonitrile or of mixed polymersof acrylonitrile and other unsaturated compounds with water-solubleorganic dyestuffs by the-cuprous ion method. Briefly stated, the processconsists in introducing into the dye-bath or into the circulatory pathof the dye liquor, metallic copper in the form of sheets, chips, wire ornetting, and carrying out the dyeing in the presence of a water-solublecupric compound, it being possible to use, instead of the copper sheets,chips, wire and/or netting, a dyeing container which is copper surfacedor which consists partly or wholly of copper.

The new process is free of the defects inherent in the known processes.Thus no copper spots are produced on the t extile material; unleveldyeings are also avoided,

I sincethe state of reduction'ofthe copper compound in the dye-bath isnot suddenly changed. Of particular importance, however, is thefact thatit is superfluous to check the state of reduction of the copper compoundby continuous measurement of the redox potential. .This

significantly simplifies the process and thus involves an appreciablesaving in dyeing costs.. The success'of the new process could not beforeseen ,because, even today, precisely what takes place in the dyeingprocess is not entirelyunderstood.

A large number of known water-soluble organic dyestuffs is suitable foruse -in the process according to the invention. As preferredwater-soluble organic dyestuffs,

there are mentioned, solely lpy way of example, the direct dyestuffs,.the acid ,dyestuffs'of the anthraquinone series groups,and particularlyof the last-named group, are

partly sensitive to the action of copper salt and atmospheric oxygen sothat dyeings thereof on polyacrylonitrile articles may be somewhatclouded. This is particularly the case when it is necessary, for onereason or another, to extend the dyeing period beyond the normal time.In such cases it is advantageous to add to the dye-baths according tothe present invention a mild reducing agent of the type of sugar, as forexample glucose, sucrose or dextrin. In the presence of such reducingagents, clouding of the dyeings, which might otherwise occur for theabove explained reasons, is avoided. This expedient o1" dyeing in thepresence of mild reducing agents constitutes a further aspect of thisinvention. I Still another phase of the invention is constituted by thedye-baths which, as already indicated, contain (i) metallic copper inthe form of sheets, chips, wire, netting or the like, (ii) awater-soluble cupric compound, and,

in some cases, (iii) a mild reducing agent of the above described type.

As cupric compounds, the most suitable for use in the present processare the water-soluble copper salts such as copper formate, copperacetate, and especially copper sulfate. At least half of the quantity ofthe copper ions necessary for the dyeing are added in this form to thedye-bath. The other half is supplied by the metallic copper according tothe equation The practically necessary quantity of copper metal surfaceand copper ions depends however upon the necessity of completing thedyeing in a practical period of time.

The dyeing is preferably carried out at pH valuesbetween 2 and 7,realized by the addition of water-soluble acid, for example formic acid,to the dye-bath. Preferred dyeing temperatures are those between 90 and130 C.

The following examples set forth representative embodiments of theinvention, without however restricting the latter. Thus, for example,the process is not at all limited to the dyeing of polyacrylonitriles,but'is also useful in dyeing mixed polymers of acrylonitrile and otherunsaturated compounds, such as vinyl halides, vinyl acetate, acrylicamides and many others. In the examples, the parts are parts by weight;the temperatures are in degrees centigrade. Percentages ,are also byweight.

Example 1 I 100 parts of a washed skein or hank of polyacrylonitrile(staple fiber) are introduced at 70 into a dye-bath which contains 20parts of a copper screen or netting made of wires of 0.2 mm. diameterand which also contains a solution of 1 part of sodium1-amino-4-phenylaminoanthraquinone-2-sulfonate, 1 part of crystallinecopper sulfate, 4 parts of concentrated formic acid and 4000 parts ofwater. The bath is heated to boiling; at the end of an 80-minute boilingperiod, the bath is completely exhausted and the textile material isdyed a fast bright blue.

A dye-bath which contains either only copper metal or only'coppersulfate solution will leave the textile material practically uncolored,when dyeing accordingto the process of the preceding paragraph. 1

Example culated through-the apparatus in which it is rapidly raised toboiling temperature, 10 parts of a copper wire screen made of wires-of0.2-mm. diameter being interposed in the circulation path of the liquor.3' The temperatureof the liquor is then slowly raised so that it reaches120 in the course of one hour. At the end of this dyeing period, thecoil of material is dyed a fast deep green. The dye-bath is completelyexhausted.

Example 3 100 parts of a fabric, consisting of a mixed polymer of 40%polyacrylonitrile and 60% polyvinyl chloride, are dyed with 3000 partsof a dye liquor containing 3 parts of Roccellin (Schultz,Farbstofftabellen No. 206), 3 parts of formic acid, 20 parts of a coppersheet of a thickness of 0.2 mm. and 2 parts of crystalline coppersulfate. The dyeing takes place at boiling temperature and yields a deepvivid red shade. The dye penetration of the very dense fabric iscomplete.

Example 4 parts of polyacrylonitrile fiber (staple fiber) are dyed in4000 parts of a dye-bath containing 2 parts of Orange R (Schultz,Farbstotftabellen No; 198), 2 parts of crystalline copper sulfate, 4parts of 85 formic acid, 20 parts of glucose and 20 parts of a nettingof copper wire of 0.2 mm. diameter. The dyeing process is ended after a2-hour boiling period and yields a very pure orange shade.

Example 5 Example 6 100 parts of polyacrylonitrile (staple fiber) aredyed at 99 in 4000 parts of a dye-bath containing 2 parts of Tuchrot BB(Schultz, Farbstofitabellen No. 548), 2 parts of crystalline coppersulfate, 4 parts of 85% formic acid, 20 parts of glucose and 50 parts ofsheet copper of a thickness of 0.2 mm. The dyeing process is completedat the end of 1 and /2 hours and yields a pure deep red dyeing.

. V Example 7 I The dyeing process according to Example 6 is repeatedexcept that the 20 parts of glucose are replaced by 20 parts of sucrose.A pure deep red dyeing is obtained.

Example 8 A pure deep red dyeing is also obtained when, as in Example 6,the 20 parts of glucose are replaced by 20 parts of dextrin.

Having thus disclosed the invention, what is claimed is:

1; A process for dyeing polyacrylonitrile with a watersoluble acidorganic dyestuff containing at least one sulfonic acid group, whichcomprises subjecting the polyacrylonitrile to the dyeing action of thedye-stuff in an aqueous dyebath initially containing, as sole metallicingredients, metallic copper and cupric ions, whereby cuprous ions areformed in situ in said bath and the dyeing is carried out in thepresence of such cuprous ions.

2. A process for; dyeing a member selected from the group consisting ofpolyacrylonitrile and copolymers of acrylonitrile with anotherv singlyunsaturated compound containing an olefinic double bond and at least 40%by weight ofacrylonitrile with a water-soluble acid organic dyestutfcontaining at least one sulfonic acid group, which comprises subjectingthe said fibers to the dyeing action of the dyestuif in an aqueousdye-bath initially containing, as sole metallic ingredients, metalliccopper and cupric ions, whereby cuprous ions are formed in situ in saidbath and the dyeingis carried out'in the presence'of such cuprous ions.i i

' 39A processfor dyeing a copolymer of acrylonitrile withanother singlyunsaturated compound-containing an olefinic double bond and at least 40%by weight of acrylonitrile with a water-soluble acid organic dyestuficontaining at least one sulfonic acid group, which com prises subjectingthe said polymer to the dyeing action of the dyestufi in an aqueousdye-bath initially-containing, as sole metallic ingredients, metalliccopper and cupric ions, whereby cuprous ions are formed in situ in saidbath and the dyeing is carried out in the presence of such cuprous ions.

4. A process according to claim 1, wherein the metallic copper is in theform of sheet copper.

5. A process according to claim 1, wherein the metallic copper is in theform of copper chips.

6. A process according to claim 1, wherein the metallic copper is in theform of copper wire.

7. A process according to claim 1, wherein the metallic copper is in theform of netting.

8. A process for dyeing polyacrylonitrile with a watersoluble acidorganic dyestutf containing at least one sulfonic acid group, whichcomprises subjecting the polyacrylonitrile to the dyeing action of thedyestufi in an aqueous dye-bath initially containing, as sole metallicingredients, cupric ions in contact with metallic copper, wherebycuprous ions are formed in situ in said "bath and the dyeing is carriedout in the presence of such cuprous ions.

9. A process for dyeing a member selected from the group consisting ofpolyacrylonitrile and copolymers of acrylonitrile with another singlyunsaturated compound containing an olefinic double bond and at least 40%by weight of acrylonitrile with a water-soluble acid organic dyestuficontaining at least one sulfonic acid group, which comprises subjectingthe said fibers to the dyeing action of the dyestufi in an aqueousdye-bath initially containing, as sole metallic ingredients, cupric ionsin contact with metallic copper, whereby cuprous ions are formed 6 insitu in said bath and the dyeing is carried out in the presence of suchcuprous ions.

10. A process for dyeing a copolymer of acrylonitrile with anothersingly unsaturated compound containing an olefinic double bond and atleast by weight of acrylonitrile with a water-soluble acid organicdyestuft containing at least one sulfonic acid group, which comprisessubjecting the said polymer to the dyeing action of the dyestufl in anaqueous dye-bath initially containing, as sole metallic ingredients,cupric ions in contact with metallic copper, whereby cuprous ions areformed in situ in said bath and the dyeing is carried out in thepresence of such cuprous ions.

11. A process according to claim 8, wherein the dyebath is contained ina container, at least those surfaces of the latter which are in contactwith the bath comprising metallic copper.

12. A process according to claim 8, wherein the dyebath also contains asugar.

13. A process according to claim 8, wherein the dyebath also containsglucose.

14. A process according to claim 8, wherein the dyebath also containssucrose.

15. A process according to claim 8, wherein the dyebath also containsdextrin.

16. A process according to claim 1, wherein the dyebath is constitutedby a circulating dye-liquor.

References Cited in the file of this patent UNITED STATES PATENTS BlakerSept. 22, 1953 Glaze Jan. 3, 1956 OTHER REFERENCES

1. A PROCESS FOR DYEING POLYACRYLONITRLE WITH A WATERSOLUBLE ACIDORGANIC DYESTUFF CONTAINING AT LEAST ONE SULFONIC ACID GROUP, WHICHCOMPRISES SUBJECTING THE POLYACRYLONITRILE TO THE DYEING ACTION OF THEDYE-STUFF IN AN AQUEOUS DYE-BATH INITIALLY CONTAINING, AS SOLE METALLICINGREDIENTS METALLIC COPPER AND CUPRIC IONS, WHEREBY CUPROUS IONS AREFORMED IN SITU IN SAID BATH AND THE DYEING IS CARRIED OUT IN THEPRESENCE OF SUCH CUPROUS IONS.